I am thinking it is time to deal backwards detective work. I suggest beginning by comparing parts on the deck to the Deere dimensions. I would suggest measuring the dimensions on the pullies currently installed then look at what Deere calls for.

Here are the dimensions for the proper Deere pulley used on the idler and the tensioner:

Also, Deere says the pullies on the spindles are 4" on the 39 deck. The larger pulley from a 47 deck will work on the same spindle so I would also suggest checking measurements on the spindle pullies. Also, swapping spindles from one deck to another is as simple as loosening 3 bolts. One more though - larger pullies on the spindles will slow blade speed on the smaller deck with shorter blades.

Also, noticed this between the older 39 and the newer 39,

Part # Serial range Length

M45998-176558 (A) DRIVE (39) 2.111 M (83.10")

M47043176559- (A) DRIVE (39) 2.014 M (79.30")

Also, the Deere idler/tensioner pullies I have used were black since they were used on MULTIPLE applications (decks, snowblowers, etc)

One last thought - something makes me think the spindles and pullies were from a larger deck. They were used to replace the original spindles with bad bearings. I could be wrong...

Attached Thumbnails

I am thinking it is time to deal backwards detective work. I suggest beginning by comparing parts on the deck to the Deere dimensions. I would suggest measuring the dimensions on the pullies currently installed then look at what Deere calls for.

Here are the dimensions for the proper Deere pulley used on the idler and the tensioner:

Also, Deere says the pullies on the spindles are 4" on the 39 deck. The larger pulley from a 47 deck will work on the same spindle so I would also suggest checking measurements on the spindle pullies. Also, swapping spindles from one deck to another is as simple as loosening 3 bolts. One more though - larger pullies on the spindles will slow blade speed on the smaller deck with shorter blades.

Also, noticed this between the older 39 and the newer 39,

Also, the Deere idler/tensioner pullies I have used were black since they were used on MULTIPLE applications (decks, snowblowers, etc)

One last thought - something makes me think the spindles and pullies were from a larger deck. They were used to replace the original spindles with bad bearings. I could be wrong...

Save the diagram I attached then print it for your reference.

I measured them, The pulley that moves with the Spring attached is 4 1/8" and the upper pulley is 4 1/8" and the 3 spindles are 4" So by what you say above, it appears that pulleys are correct?, so JD has made the belt per the Parts MAnual not long enough, SO I should go tell JD there belt isn't long enough

Went up to John Deere today, I showed them the diagram REV gave me and I took a pic of the belt NOT fitting, and I took my Serial Numbers, they researched it and REV was right that's the P/N BUT it wont fit, they said are you sure your deck is not a 47"? I said even if it is that is still the right P/N belt!! They said yea your right. They refunded my money, now I have to go to NAPA.

P.S. I verified that I have the right pulleys, I took apart the Patio deck and yep my pulleys are all the same

Napa ordered me the belt, I think they said the number on it was a 50" I pick it up tomorrow $25.99 Same as the JD OEM belt price, I tried the old NAPA belt again tonight and it fits really nice and tight when tensioned up.

Received belt from NAPA total was $29.00 with tax. Installed the belt fits great. So if you need a belt for the 39" or 47" mower deck the NAPA Part Number B87 50 it says industrial belt so it should be strong.

Installed cover with the new nuts washers and lock washers. Working on painting connecting arms now, then I have to get the blades sharpened